The invention relates to nuclear medicine imaging systems, and more particularly relates to collimators used with gamma cameras in the detectors of nuclear medicine imaging systems. In its most immediate sense, the invention relates to a method and apparatus for the transfer, removal, mounting and storage of collimators in nuclear medicine imaging systems.
Nuclear medicine imaging assesses the radionuclide distribution within a patient after the in vivo administration of radiopharmaceuticals. Imaging systems that assess radionuclide distribution include radiation detectors and acquisition electronics. The imaging systems detect x-ray or gamma ray photons derived from the administered radionuclides. Single photon emission imaging and coincidence imaging are two forms of nuclear medicine imaging that are currently in common use. In single photon emission imaging, the radionuclide itself directly emits the radiation to be assessed. For example, in Single Photon Emission Computed Tomography (SPECT), y-emitting radionuclides such as 99mTc, 123I, 67Ga and 111In may be part of the administered radiopharmaceutical.
Detectors used in such single photon emission imaging often use collimators placed between the patient and the gamma ray camera of the detector. The purpose is to eliminate all photons but those photons traveling in a desired direction. For example, a parallel hole collimator eliminates photons traveling in all directions except those almost perpendicular to the surface of the detector. The energy of emitted photons as well as their location of origin may then be accumulated until a satisfactory image is obtained.
Coincidence imaging eliminates the need for such a collimator by relying on the detection of two photons at different detectors at nearly the same time. An example of coincidence imaging in current clinical use is Positron Emission Tomography (PET).
Radiation detectors used in nuclear medicine imaging need to absorb x- or gamma-ray photons in an energy range typically between 1 keV and several MeV. These imaging photons are the photons either directly emitted or resulting from radionuclides within a patient. In order to stop imaging photons of these energies with a collimator in SPECT imaging, a material with a high density and a high atomic number (Z) is necessary. Lead is the most common material used for collimators, but other materials such as tungsten may also be used.
Radiation detectors for SPECT imaging systems often have the ability to use collimators which may be mounted or removed from the system detectors. These “mountable” detectors are useful because a collimator with a different geometry may yield higher quality images in different situations. Being able to “swap in” a collimator with a specific geometry is thus highly advantageous.
As mentioned above, collimators need to be made of a material with a high density and a high atomic number in order to effectively stop imaging photons. These materials, such as lead, are very heavy. For example, a typical lead collimator may weigh on the order of several hundred kilograms. This high weight creates many problems for the effective and efficient imaging of patients when collimators which are mountable are in use. One problem is the risk of damage to either the gamma camera system within the detector, or even damage the collimator itself, when physically removing or mounting the collimator into the detector. Another problem is the risk of injury to the medical technician performing the mounting or removal of the collimator. Another problem is the time required to remove an old collimator and mount a new one in a detector. These procedures time increase the set up time for a patient scan, and reduce the throughput of patients of an imaging system, a determining factor in the profitability of an imaging system. In addition, transferring a collimator from a storage location to the imaging system may also increase the set up time for a patient scan. Another problem is that bulky and heavy collimators often require additional floor space for storage. Another problem is that removing and mounting collimators often requires that components of an imaging system, such as a patient handling system, be moved from their standard operating position. This also increase the time required for patient setup.
Various attempts have been made to address the above problems. However, none of the currently available solutions adequately address the problems of using mountable collimators. Their remains a need in the nuclear medicine imaging art for systems and methods of reducing the danger, time, space, and expense of using modular collimators.